Yoler, U.S. Pat. No. 2,783,684 and Yoler et al, U.S. Pat. No. 2,790,354 disclose high pressure, high temperature plasmas that are applied to a rear face of a projectile in a barrel bore, to accelerate the projectile in the bore. The plasma applied to the bore behind the projectile is derived by applying discharge voltages to a solid hydrocarbon tube located along the length of a barrel forming the bore. A series of such tubes is longitudinally disposed along the length of the barrel. The projectile is accelerated along the length of the barrel by providing discharge voltages along each tube in synchronism with movement of the projectile along the length of the bore. A discharge voltage is applied to each tube immediately after the projectile has traversed that particular tube. The plasma discharges establish a very high pressure behind the projectile to provide the driving force for the projectile.
Goldstein et al, U.S. Pat. No. 4,590,842, discloses a further system wherein a projectile is accelerated by applying plasma to a barrel bore through which the projectile is accelerated. The plasma is applied at plural longitudinal positions along the length of the bore by plural plasma sources positioned at an oblique angle with respect to the bore longitudinal axis. Each plasma source includes an elongated, capillary sleeve having a dielectric wall from which plasma is formed by an ablation process in response to a discharge voltage applied between spaced electrodes of the capillary passage. A capillary passage is a passage having a length to diameter ratio of at least 10:1. The plasma from each of the capillary sources having an oblique angle with respect to the barrel bore is applied to the rear of the projectile, to accelerate the projectile to a high velocity, such as a few kilometers per second. A capillary discharge can also be used to initiate movement of the projectile, by locating the capillary passage so it is coaxial with the barrel bore, as disclosed in U.S. Pat. No. 4,715,261.
In the copending, commonly assigned, Tidman et al U.S. Pat. application Ser. No. 06/929,365 filed Nov. 12, 1986, entitled "Apparatus For and Method of Accelerating A Projectile Through A Capillary Passage and Projectile Therefor," now U.S. Pat. No. 4,907,487 a projectile is initially accelerated by applying a discharge to a fluid substance in a capillary passage to form a plasma. A discharge is then established between electrodes at opposite ends of the capillary passage to further accelerate the projectile. Additional energy is imparted to the plasma at a position downstream of the initial starting location by ohmically heating the plasma as it traverses this location. The ohmic heating is obtained by applying eddy currents to the plasma with a solenoid coil surrounding the bore through which the projectile is accelerated.
A problem with devices of the type disclosed by Yoler et al and Yoler, and to a certain extent the other, previously described multi-stage projectile accelerators, is that the plasma applied to an intermediate location along the length of the barrel bore has a tendency to flow into the region of the bore substantially behind the projectile, i.e., into the volume of the bore between the projectile and the breech of the barrel. Because the plasma expands into the volume behind the projectile, the pressure exerted against the rear of the projectile is not as great as if the plasma were confined between the intermediate location and the rear of the projectile.
It is, accordingly, an object of the present invention to provide a new and improved apparatus for and method of accelerating a projectile by applying a high pressure plasma to the rear of the projectile as it is accelerated in a bore of a barrel, wherein the tendency of the plasma to expand into the volume of the bore behind the projectile is substantially overcome.
Another object of the present invention is to provide a new and improved apparatus for and method of activating a valve synchronously with the application of a plasma to a projectile that is accelerated in a barrel bore by the plasma to prevent the expansion of plasma to a volume behind the region where the plasma is applied to the projectile.
Another object of the invention is to provide an apparatus for and method of substantially preventing plasma that is applied to a bore of a barrel to accelerate a projectile in the barrel from flowing between an application region of the plasma to a volume behind the application region, with a valve means having no moving parts.
The importance of a valve means having no moving parts to prevent the expansion of plasma into a volume behind the projectile is paramount because of the very high speed, for example on the order of kilometers per second, of the projectile and the associated high sound speed of the main constituent, preferably hydrogen, of the plasma. There are obvious difficulties associated with physically moving a valve into position to prevent the expansion of the plasma for projectiles and gases having the stated speed magnitude.
In the copending, commonly assigned application of Goldstein et al, U.S. Pat. application Ser. No. 07/252,551, filed Oct. 3, 1988, entitled "Plasma Propulsion Apparatus and Method," substantially constant pressure is provided for a plasma accelerating a projectile along a barrel bore by linearly increasing the power supplied to a single capillary plasma discharge at one end of the bore. While this technique functions admirably, it requires a specialized, programmed power supply and relatively large peak currents as the projectile approaches the barrel muzzle.
It is, accordingly, a further object of the present invention to provide a new and improved apparatus for and method of accelerating a projectile in a barrel bore, wherein the pressure of the plasma is maintained at a high average value as the projectile traverses the bore through the use of a conventional power supply.
A further possible problem with the prior art devices is that the pressure in the bore can exceed the rupture pressure of a solid dielectric sleeve lining the barrel bore.
It is, accordingly, a further object of the present invention to provide a new and improved apparatus for and method of accelerating a projectile in a barrel bore, wherein the pressure of the plasma is automatically regulated so it cannot exceed a predetermined value that is likely to cause rupture of a component of the barrel bore.